Use backticks not vertical bars to denote variables in comments for /api

Bug: webrtc:12338
Change-Id: Ib97b2c3d64dbd895f261ffa76a2e885bd934a87f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/226940
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34554}
diff --git a/api/video_codecs/video_decoder_factory.h b/api/video_codecs/video_decoder_factory.h
index 0b6ea4f..ef90809 100644
--- a/api/video_codecs/video_decoder_factory.h
+++ b/api/video_codecs/video_decoder_factory.h
@@ -40,7 +40,7 @@
   // power efficient, which is currently interpreted as if there is support for
   // hardware acceleration.
   // See https://w3c.github.io/webrtc-svc/#scalabilitymodes* for a specification
-  // of valid values for |scalability_mode|.
+  // of valid values for `scalability_mode`.
   // NOTE: QueryCodecSupport is currently an experimental feature that is
   // subject to change without notice.
   virtual CodecSupport QueryCodecSupport(